Disc drive machines record and reproduce information stored on concentric circular or spiral tracks on magnetic or optical discs. Tracks are written and read by magnetic heads which must be accurately positioned over one of the tracks on the surface of the disc.
The common form of rotary actuator includes a head arm, flexure, read/write transducer and actuator arm extending out from a pivot. Extending from the pivot to essentially form a V-shaped arm assembly is an actuator arm which in turn is coupled to an actuator motor. Known rotary actuator mechanisms require a stable pivot mechanism to support the actuator arm and head support arm.
The pivot mechanism in prior art rotary actuators generally consists of a shaft supporting the juncture of two arms, i.e., an actuator drive arm coupled to the actuator motor and head arm. This shaft may include, to maintain the actuator arm alignment, two high precision ball bearings, spring retainers, preload springs, plus attachment means to the base casting and the arm or arms.
The pivot point of the actuator arm is typically mounted for rotation about a fixed pivot point. However, assembly of this pivot mechanism is expensive and time consuming to accomplish with proper alignment and a tight fit between arm and pinion. It has previously been proposed, in the above-referenced patent application, to springload the pivot point of the actuator arm, thereby biasing the rack or sector gear at the head end of the arm against the pinion carried on the surface of the actuator motor shaft. However, it is difficult to maintain sufficient spring force for an extended period of time. Under shock and vibration conditions along the axis of the actuator arm, the arm was subject to sudden unloading from the face of the pinion. Further, the preload created by the steel suspension against the arm tends to change with time; in fact, as parts wear the pivot point may effectively move.
Another integral portion of any actuator mechanism is a transmission coupling between actuator motor shaft and drive arm while maintaining a mechanical resonance above the electrical band pass requirements. Typically, the motor shaft is located perpendicular to the actuator arm and coupled thereto through bands which wind and unwind on the pulley with rotation of the shaft, thereby moving the actuator arm back and forth.
An objective herein is to eliminate drive bands used to couple the actuator motor to the actuator arm to control track accessing. Prior efforts have been made in this direction by providing a frictional coupling between a sector at the end of the actuator arm and the motor shaft. However, such a connection is clearly subject to misalignment in the event of shock, and accurate realignment can be quite difficult. Also, the frictional coupling effect can diminish with time and particles can be shed from this coupling transmission that are harmful to the operation of the drive transmission.